Unusual stereoselectivity of methionine-γ-lyase from Citrobacterfreundii toward diastereomeric (S)-methionine S-oxide

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Expedient Strategy for the Synthesis of 5-Acylethynylpyrrole-2-carbaldehydes

5-Acylethynylpyrrole-2-carbaldehydes have been synthesized from the protected pyrrole-2-carbaldehydes by their transition-metal-free topochemical mechanoactivated ethynylation with acylbromoacetylenes in a solid Al₂O₃ medium (room temperature, 6 h, 41–54% yields).     

Environmental radioactivity of soils and sediments: Egyptian sector of the Nile valley

The activity concentrations of natural ⁴⁰K, ²³²Th, and ²³⁸U in 89 soil and 84 sediment samples collected over the entire Egyptian Nile River basin including the Nile delta are reported based on the results of epithermal neutron activation analysis. The average activity concentrations of ⁴⁰K, ²³²Th, and ²³⁸U equal to 15.3?±?6.6, 15.6?±?11.1 and 220?±?31 Bq/kg, respectively, are significantly lower than those reported for the Upper Continental Crust, World Average Sediments as well as World Average Soils, suggesting the presence of a considerable portion of mafic material, most probably originating from the Ethiopian High Plateau. Their average activity concentrations are statistically the same in soil and sediments, indicating that the Nile sediments and soil material are of the same origin. The main goal of this study was not only to estimate the radiological hazards but also to show the influence of sedimentary material transportable by the Blue Nile from the Ethiopian High Plateau. The different hazard indices like the radium equivalent, gamma index, external hazard as well as the internal hazard show a low radiological exposure either on direct contact or if local mud bricks are used in the construction of dwellings.     

New insights into water‐soluble and water‐coordinated copper 15‐metallacrown‐5 gadolinium complexes designed for high‐field magnetic resonance imaging applications

The development of contrast agents specifically designed for high‐field magnetic resonance imaging (MRI) is required because the relaxation efficiency of classic Gd(III) contrast agents significantly decreases with increasing magnetic field strengths. With an idea of exploring the unique structure of lanthanide (Ln) 15‐MC‐5 metallacrowns, we developed a series of water‐soluble Gd(III) aqua‐complexes, bearing aminohydroxamate (glycine, α‐alanine, α‐phenylalanine and α‐tyrosine) ligands, with increasing number of water molecules directly coordinated to the Gd(III) ion: Gd(H₂O)₄[15‐MC_Cu(II)Glyha‐5](Cl)₃ ( 1 (Gd)), Gd(H₂O)₄[15‐MC_Cu(II)Alaha‐5](Cl)₃ ( 2 (Gd)), Gd(H₂O)₃[15‐MC_{Cu(II)Phalaha}‐5](Cl)₃ ( 3 (Gd)) and Gd(H₂O)₃[15‐MC_Cu(II)Tyrha‐5](Cl)₃ ( 4 (Gd)). In these systems, the Ln(III) central ion is coordinated by five oxygen donor atoms of the ligands and three or four inner‐sphere water molecules. The X‐ray crystal structure of metallacrown Ln(H₂O)_3,4[15‐MC_Cu(II)Rha‐5]³⁺ agrees with density functional theory predictions. The calculations demonstrate that the exchange of coordinated water molecules can proceed easily, resulting in increased relaxivity parameters. The longitudinal relaxivities (r₁) of 1 (Gd)– 4 (Gd) in water at ultrahigh magnetic field of 9.4 T were determined to be 11.5, 14.8, 13.9 and 12.2 mM^?1 s^?1, respectively. The ability to increase the number of Ln(III) inner‐sphere water molecules up to four, the planar metallacrown structure and the rich hydration shell due to strong hydrogen bonds between the [15‐MC‐5] moiety and bulk water molecules provide new opportunities for potential MRI applications.     

A new synthesis of 4′-trifluoromethyl-2,2′:6′,2″-terpyridine

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